Data broadcast method

ABSTRACT

A system for providing requested data sets of broadcast data service transmitted as part of a broadcast signal, including a broadcast headend configured to receive a data request from a receiver, and configured to broadcast requested data sets to the receiver in response to the data request from the receiver, a processor configured to periodically extract all of the requested data sets of the broadcast data service from a broadcast carousel included in the broadcast signal, a memory configured to store all of the requested data sets of the broadcast data service, defining a plurality of digital-audio/video-data-sets including television clips, a first controller configured to allow selection from a list of the plurality of sets of the digital-audio/video-data-sets, and a second controller responsive to a user initiated selection signal to cause the memory to output a user selected one of the plurality of digital-audio/video-data sets selected from the list, wherein the processor converts the digital-audio/video-data of the requested data sets of the broadcast data service into real time audio/video data.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. patent application Ser. No. 09/630,971,filed Aug. 1, 2000, the entire contents of which is incorporated hereinby reference. U.S. application Ser. No. 09/630,971 claims the benefit ofpriority under 35 U.S.C. §119 from United Kingdom Patent Application No.9918284.2, filed Aug. 3, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a data broadcast system and method and,more particularly, to a method of broadcasting data services withbroadcast signals and a system for selectively providing portions of thebroadcast data service to the user.

2. Description of the Related Art

Digital television systems have become widely used for broadcastsystems. The digital television systems provide digitisation andcompression of the image to be broadcast with technologies such asMPEG-2 compression. The broadcast pictures are hence encoded andconveyed to the digital television receivers in the home as a digitaldata sequence. Digital television has a number of advantages overconventional analogue television, such as increased capacity andincreased robustness to noise and interference.

Digital television systems also allow many kinds of data to be carriedseamlessly within broadcasts carrying audio and visual data. Hence, manynew services can be provided through the digital TV receiver to theviewer.

A popular analogue service that uses additional data carried within thebroadcast transmission is the teletext service. The teletext service iscarried as digital data within certain transmission lines of thevertical blanking interval (VBI) of the TV signal. The VBI is the timeallowed for the raster scan to return to the top of the screen and hencethis time is not used to carry any useful picture information. Somelines are set aside for teletext data and the digital data is modulatedonto the broadcast TV signal.

Teletext systems broadcast a number of “pages” of data in cycles with apage being typically updated every 2 to 3 minutes. The update cycle timedepends on how many pages are broadcast in the cycle, there being only asmall bandwidth available for the teletext data. Upon selecting a page,the viewer has to then wait for the page to be delivered as part of thecycle—this time will be on average half the total cycle time for all thepages.

Typical teletext systems provide the latest news, sport and TV guideinformation and also reference information and advertising. Teletextsystems are very useful for providing “headline” information such assports results when there is no other means of obtaining theinformation.

A very popular use for the teletext systems is to find out the latestinformation for some rapidly changing event such as a sports event.Often this can be the only way the viewer can obtain this information,because sports events are often not screened live, are carried as partof a pay-per-view service or have finished such that the programs arenow carrying other content. Hence, this allows the viewer to catch upwith “missed” content such as sports events or news broadcasts by othermeans using the data services.

A problem with previous broadcast data services is that they communicatevery little information—perhaps just the score of a football match forinstance. The user, although not wanting to see the whole sports event,would like a little more information than just the score—maybe to seevideo of the goals or near misses in the example of a football match.

However, to provide a service like this there are further problems.Simple data services such as teletext can be provided easily with a lowbandwidth. Providing an enhanced data service with audio and visual datawould require more bandwidth or take a lot longer to update and cyclethe information.

Viewers have different interests and priorities, so what is important toone viewer is of little interest to another. Screening news “highlights”in a sequence that repeats and updates every 15 minutes is not appealingto a viewer if they have one item they would like to see and have towait an average of 7.5 minutes to see this item.

Digital broadcast systems can provide more bandwidth for programcontent. However, this bandwidth is still at a premium. Using some ofthe bandwidth to provide broadcast data services can be consideredwasteful, particularly if there is other content that could be screenedat the same time to a reasonable audience. Indeed, screening live videoand audio as a broadcast data service will still take up approximately 2Mbit/s of bandwidth using MPEG-2 compression.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to overcome the problemsidentified above.

According to the present invention, there is provided a method ofbroadcasting a broadcast data service together with broadcast digitaltelevision data as part of a broadcast signal, the broadcast dataservice including television data. The method comprises broadcasting thetelevision data of the broadcast data service as non-real time data.

In this way, it is possible to allocate a relatively small bandwidth tothe broadcast data service and yet allow television clips to be replayedby a receiver as part of the broadcast data service. The televisionclips may be transmitted in non-real time over an extended period andthe data assembled in the receiver for display.

The method may further comprise processing and/or compressing a block ofthe television data as a whole.

Thus, compared to continuous processing or compression processes such asMPEG, a television clip or sequence may be taken as a whole beforecompression. This may enable much greater compression to be achievedthan for the continuous processes used in normal broadcasting.

The block may comprise data requiring off-line decoding.

In particular, it is possible to compress a block of data representing atelevision or video sequence, broadcast it in non-real time and thenstore the data in a memory associated with the receiver. It is thenpossible to post process or decompress the data off line.

Preferably, the method comprises, during normal broadcasting, onlybroadcasting portions of the broadcast data service required to replaceprevious respective portions which have been changed such that receiversof the broadcast signal may store all of the current portions of thebroadcast data service and update the stored portions according toreplacement portions received with the broadcast signal.

In this way, the bandwidth required for maintaining an enhancedbroadcast data service may be reduced, such that the cycle time may alsobe kept to a minimum. Furthermore, since receivers may use a memory tostore the entire broadcast data service, near instantaneous access ispossible for the users.

According to the present invention, there is also provided a system forselectively providing portions of a broadcast data service transmittedtogether with broadcast digital television data as part of a broadcastsignal, the portions including data portions having digital televisiondata in non-real time. The system comprises a processor for extractingportions of the broadcast data service available from the broadcastsignal, a memory for storing all of the current portions of thebroadcast data service and a controller responsive to a selection signalto cause the memory to output selected portions of the broadcast dataservice. The processor is also for converting the digital televisiondata of data portions into real time data.

In this way, the system can receive television clips, video sequencesand the like over the relatively narrow bandwidth used for the broadcastdata service and, by storing the relevant portions in the memory, canprocess those portions to return the data to real time.

Preferably, the digital television data of the data portions iscompressed and/or processed and the processor processes the dataportions off line.

In this way, it is possible to make further use of the relatively narrowbandwidth available for the broadcast data service. Television data canbe compressed to the maximum amount with little regard for the timerequired for decompression.

Preferably, the processor processes the portions at times of low usage.

The processor may be provided as a separate processor in the storagedevice.

Thus, the processor can fit in decompression and processing of anypreviously received compressed/processed television data in amongst itsother duties in the operation of the system.

The processor may operate directly on the data in the memory. However,it is also possible for the processor to operate in a batch processingmethod with data loaded locally from the memory in small chunks. Thismay be particularly appropriate where the memory is provided separatelyfrom the processor and the processor has its own working memory.

The processor may conduct processing using a predefined protocol.

Thus, any processing or compression of the data might make use of anexisting protocol such as “WinZip”.

Alternatively, the processor could conduct processing using a downloadedprotocol. This might provide greater flexibility to a system and/orprevent unauthorised decompression of the data.

Similarly, the processor could conduct off line decryption of data usinga key. The key could be downloaded by broadcast or other means such as amemory stick or smartcard.

Preferably the controller is also for identifying correspondingextracted and stored portions and for replacing data portions stored inthe memory with respective portions extracted from the broadcast signal.

Thus, at the receiving end, a user's device continually updates thestored complete broadcast data service and is able to retrieve anydesired selected portions of the broadcast data service in a nearinstantaneous manner.

Preferably, the method of broadcasting includes additionallybroadcasting all of the current portions of the broadcast data serviceto enable a user to obtain all portions of the broadcast data servicesoon after initial connection. This may be achieved by using a separatededicated channel or by periodically using an expanded bandwidth at atime of low demand for the broadcast digital television data.

The system may be provided with additional means for accessing thecomplete broadcast data service from a different channel.

In this way, after a receiving system has been disabled for some time orhas first been connected, the memory can be filled with the currentversion of the broadcast data service for future update.

The receiving system may be constructed as a single integral unitcomprising a digital television receiver. Alternatively, variouscomponents of the system may be constructed separately and linked bymeans of a network, such as using an IEEE 1394 interface.

In this way, a single television receiver/display could provide all ofthe functions of the present invention. Alternatively, atelevision/display could be connected by means of an IEEE 1394 interfacewith a broadcast data service unit which either has its own receiver ormakes use of the receiver of the television display to obtain thebroadcast data service portions. Similarly, the memory could be providedin the broadcast data service unit or separately, for instance againconnected with an IEEE 1394 interface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a system for receiving broadcast data servicesaccording to the present invention;

FIG. 2 illustrates a system for receiving broadcast data servicesaccording to the present invention; and

FIG. 3 illustrates the periodic transmission of a complete broadcastservice.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will be more clearly understood from the followingdescription, given by way of example, with reference to the accompanyingdrawings.

The MPEG video and audio compression system is designed to provide amaximum amount of compression in a broadcast environment. The MPEG videoand audio compression system is also designed to allow the decompressionto be carried out with a limited amount of memory in the receiver. Thisallows the decompression system in the receiver to be implemented withless memory and processing—and hence more cheaply—than the compressionsystem in the transmission head-end.

Even though the digital encoding of information allows many morechannels to be transmitted, there is still a limited bandwidth for thetransmission of the information. Hence MPEG audio and video channels areconstrained to a certain bit rate dependent on the bit rate available.

There is a trade off between the number of channels carried and thevideo quality (dependent on the bit rate of the compressed video andaudio signals) of the channels.

Many new services other than just audio and video services can now alsobe provided using the digital television broadcasts. Data andinformation on the transmitted programs and other entirely new servicessuch as home banking or shopping can be provided.

Many of the data services are also carried in a “carousel” where thedata is broadcast in a cycle. At any one time only one part of the dataservice is being broadcast, but over a fixed period—say fifteen secondsor three minutes, all the data will be broadcast. After this period thedata is repeated either exactly the same, or with changes if any of thedata needs to be changed. This method allows receivers to receive allthe data for a service, but allows the data to be transmitted in arelatively small bandwidth.

It is considered that in the broadcast environment, many of the systemsused presently are designed to make use of the limited bandwidthavailable and also assume a limited amount of storage and processingresource in the receiver.

This is indeed true for current systems as the bandwidth is fixed andthe receivers have to be implemented as cheaply as possible to beaffordable for the average consumer.

Hence the data is broadcast assuming or knowing that the receiver has acertain limited amount of storage and processing power. This constrainsthe format and type of data that can be sent.

For instance, data requires much processing power at the receiver, ordata requiring a large amount of storage for processing at the receivercannot be sent, since it is not practical to provide a receiver

It is now proposed to use storage media such as magnetic disks andsemiconductor storage devices to provide storage for the transmitteddigital broadcasts. The use of digital storage devices provides manyenhanced applications for the user, providing a far better userexperience than that of present using conventional analogue storagetechnologies.

The AV devices in the home can be in separate physical enclosures andneeding interconnection. The key technology for interconnection ofdigital devices in the home is the IEEE1394 Serial Bus interface whichprovides a low cost, user friendly method to send audio, visual andcontrol data between devices in the home.

Hence a typical digital TV system arrangement in the home could have adigital TV receiver, display device, magnetic storage and DVD player allconnected using IEEE1394 Serial Bus connections.

Mass storage can also be alternatively or additionally providedintegrated into a consumer device—for instance an integrated digitaltelevision receiver may incorporate a large magnetic storage.

Finally, it is also possible to use a “Memory Stick”. This is anon-volatile memory held in a small package to allow data to betransferred between cameras, camcorders, PCs and other home AV devices.There are other formats also supported by other consumer electronicsmanufacturers.

FIG. 1 illustrates schematically various components of a system forreceiving a broadcast data service.

A receiver 2 is provided for obtaining and demodulating transmitted datafrom an aerial, cable, satellite or the like. The demodulated dataincludes digital television data, together with associated broadcastservice data.

Under the control of a control panel 4 or remote control, a videoprocessor 6 extracts data from a received signal for a selected videochannel and displays that video channel on the display 8.

A processor 10 is also provided for extracting any broadcast servicedata from the received signal. The processor 10 may be provided togetherwith the receiver 2, together with the memory 12, together with thecontroller 14 or separately. The data is stored in a memory 12 under thecontrol of a controller 14. A user may then select (possibly using thecontrol panel 4) desired portions of the data broadcast service. Underthe control of the controller 14, the memory 12 then outputs appropriatedata for display on the display 8.

The memory 12 can be provided as a magnetic disc, for instance as iscommonly known as a hard disc drive, a semiconductor memory or othermeans.

The system of FIG. 1 can be provided integrally within a televisionunit. However, it is also possible for various components of the systemto be distributed around a network, for instance using the IEEE 1394interface. This is illustrated in FIG. 2.

The system may be provided merely with an external storage device.Similarly, the system may be provided as a broadcast service unit forconnection to a television display and the broadcast service unit mayitself have an internal memory or use an external memory and may itselfhave a processor. Just as with an integral design, the broadcast serviceunit can obtain received digital data from the receiver, processportions of the data appropriately and provide selected portions to thetelevision display upon demand.

With regard to transmission bandwidth of a broadcast service, anaudio/visual stream can typically consume 2 Mbit/s using current MPEG-2compression technologies. This could be construed as wasteful.

By making use of the memory of the system, it is possible to broadcastthe audio and visual data at a rate slower than real time. The audio andvisual data is extracted from the broadcast data service and stored inthe memory 12 of the system. When the audio/visual data is required forplayback, the system can then retrieve the data at the required datarate allowing replay in real-time. In this way, by halving the broadcastrate of the audio/visual data, the bandwidth consumption of that portionof the service would also be halved. Although the cycle time wouldtherefore also be doubled, by means of the memory of the system, accesswould be immediate unless a user happened to request a portion while itwas being broadcast.

With the proposed mass storage technologies now being implemented inconsumer audio/video devices in the home, there are significant changesin the processing potential and storage available to the digitaltelevision receiver.

Increased storage can allow different and possibly more effectivecompression and pre-processing to be applied to broadcast data. A largeamount of storage allows broadcast to be downloaded as a whole block ofdata. This block of data is then processed as a whole, rather as abroadcast stream, where only a small fraction of the broadcast data isprocessed as it passes through the receiver. Thus, the video data can becompressed using a completely different non-streaming algorithm otherthan MPEG and be subjected to off-line compression/decompression asdiscussed.

The increased storage also allows data to be stored for laterprocessing. This effectively increases the processing power available inthe receiver. Since the data is stored “offline” the receiver can thenprocess the data as a background task or times of low usage. When thedata is fully processed then it can be made available to the user.

The video need not only be sent at slower than real time (for “tricklefeed”). It could also be sent faster than real time, for instance for amass video dump during the night.

Additionally, the data can be sent in a more interactive manner. Forinstance, there can be an almost permanent return channel connectionfrom the receiver to the broadcast headend. This headend can field therequests from the receiver population and broadcast the data (video orwhatever) according to the demand for each item.

In this case, heavily requested items are broadcast first. Oncebroadcast, the item is cached locally so that, if requested again, thereceiver displays it locally. Thus, a popular item is broadcast a lot tostart with and then the requests fall off and allow less popular itemsto be broadcast.

For a broadcast video program, it is also possible for certain sectionsto be marked as “highlights”. Just these can then be stored, or thewhole video stored, so that the highlights can be skipped between by theuser later.

The “offline” processing can be carried out in different ways

It can be carried out by the processor of the digital TV receiveroperating directly on the data on the mass storage device.

It can be carried out by the processor of the digital TV receiver in a“batch” processing method with the data loaded locally from the massstorage device in small chunks.

It can be performed by a processor local to the mass storage device.

There are a variety of ways of processing the data on the mass storagedevice to provide “post-processed” data that can then be used by thedigital TV receiver.

Post-processing or decompression of data can be conducted using anexisting pre-defined protocol such as “WinZip”.

Post-processing or decompression of data can be conducted using adownloaded protocol.

Post processing of data can be conducted to provide a new set of data.For example, processing two video streams to provide a new videostream—perhaps a “reverse angle” or “birds eye” view of a videosequence.

Offline decryption of a file can be conducted using a key provided tothe user by broadcast or other means (on memory stick or smart card).

Data may be input from another source that is then post processed usingbroadcast data.

Offline compression or processing of video data can be conducted(perhaps DV format data from a digital camcorder) for laterre-transmission by e-mail, memory stick, i.LINK, or other means.

It could also be construed as wasteful using bandwidth to cycle the samecontent only with slight updates each time rather than for “real” livecontent such as films, news and sports broadcasts.

In a service where portions of the broadcast data service are cycled,there is a trade off between the bandwidth consumed by the service andthe cycle rate. The service can offer a rapid update rate if it consumesa large amount of bandwidth. That bandwidth can be reduced, but willresult in cycle time being increased.

For the broadcast of broadcast data services, such as teletext, data iscyclically processed and provided to the user. It is now proposed toprovide enhanced broadcast data services which will include more data.Unless substantial bandwidth is used, this will result in extended cycletimes. In particular, if an enhanced service showing audio/video clipsand data has a very long cycle time, then the service will beundesirable for the intended application of a quick newsflash styleupdate on the days news or sports events.

To overcome this problem, it is proposed to store an entire cycle of abroadcast data service such that the user can display any portion of theservice instantaneously at any time. All portions of the broadcast dataservice of the cycle are stored in a memory. Indeed, the data portionsmay be obtained when a user is not viewing the broadcast data service orhas the receiver on standby.

For the user of the service, the most visible parameter is the cyclerate. The viewer will want to have up-to-date information as soon aspossible and will not want to have to wait. Hence, this is one of thekey requirements for the service. On the other hand, for the serviceprovider, the bandwidth consumed is probably the most importantparameter. The bandwidth consumed by, in particular, data broadcastservice affects the bandwidth available for other broadcast dataservices and television data itself. A reduction in the bandwidthavailable for other services is hence likely to affect the revenueavailable to the service provider.

For many broadcast data services, large numbers of the portions of abroadcast data service remain the same for each cycle. For instance, fortraditional style pages as used with teletext, most pages might remainthe same from one cycle to the next. Similarly, when transmittingaudio/visual news or sports clips with a broadcast data service, it islikely that the same clips will be provided for an extended period oftime during the day.

In order to take advantage of this fact, it is proposed to transmit onlyportions of the data broadcast service which have changed from one cycleto the next. In this way, there may be provided a relatively fast updaterate for information on the service with an efficient use of bandwidthfor the service provider.

A broadcast data service may take many different forms. It may betransmitted cyclically as a carousel of main information topics. It isalso possible that, within each topic, further data portions aretransmitted cyclically as a sub-carousel. Each data portion may consistof a traditional style page of data or may consist of other data such asimage data or audio/visual data. An entire page or audio/visual datasequence can be considered as a portion or a page or audio/visualsequence can be made up of a number of portions. Irrespective, thesystem should provide the data in portions which can be replacedindividually in such a way as to update the overall broadcast service.Hence, individual bytes of data or groups of bytes could be consideredas “portions” provided that the system allows individual replacement ofsuch portions. However, for very small portions, such as individualbytes, the protocol overhead for embodying the system is likely to beundesirably high.

For a receiver that has no previously stored content, the “differential”content will not be useful, as it will not comprise the full service.This situation will arise for instance when the memory of the broadcastservice unit is first connected to the system.

It is possible to configure the system such that over time, by storingall of the updated portions, the complete broadcast data service will beestablished. Alternatively, however, the full service could be broadcasteither on a different dedicated channel (possibly by means of anon-broadcast download service) or at times when the demand for otherconventional broadcast is lower. Referring to FIG. 3, it will be seenthat, at these times, the bandwidth allocated for those conventionalservices can be reduced. As a result, the bandwidth available for thebroadcast data services can be increased. This allows a receiver toquickly update its stored broadcast service information with the fullinformation service. Subsequently, in the normal way, the system cankeep up to date with the service using the differential update stream.

The service provided using this system could not only carry MPEG-2encoded audio and video data, but, as discussed above, could also carryinformation which has been compressed and encoded using other moresuitable or efficient protocols. For instance, a football match couldtake advantage of the fact that most of the content features a lot ofgreen with only a few small moving areas.

In this situation, an algorithm for decompressing and decoding could bedelivered to the receiver and then executed by the receiver under apre-defined protocol.

Since received broadcast service data is being stored off line and thedecoding operation does not need to be executed in real time, theprocessing requirements for the decompression and decoding are not sogreat. Hence, the receiver processor can decode the content as abackground task for display later.

It should be appreciated that the data content of the broadcast dataservice need not be limited to audio/visual data or traditional datapages. The content can be suitable for use by an interactive engine inthe receiver/broadcast service data unit. In this way, a mixed servicecould be provided featuring text, graphics and audio/visual clips.

Data portions may also comprise data requiring off-line decoding. Thedata need not necessarily be a program, but could be any sort of data.

MPEG compression and decompression systems are designed to be used in abroadcast system with limited decompression memory in the receiver, asmall delay (of the order of a second) in decode delay and a limited“pick-up” delay (where “pick-up” delay is the delay when a receiver isturned on and has to wait a few frames for a full “I-frame” when it canpick-up the transmission and start decoding).

By virtue of the present invention, it is possible to usecompression/decompression programs which rely on having the whole datafile present to be able to execute. In particular, by storing the dataoff-line, such compression/decompression becomes possible and it ispossible to provide alternative compression and decompression algorithmsto provide better performance than with current MPEG based schemes.

1. A system for providing requested data sets of broadcast data servicetransmitted as part of a broadcast signal, comprising: a broadcastheadend configured to receive a data request from a receiver, andconfigured to broadcast requested data sets to the receiver in responseto the data request from the receiver; a processor configured toperiodically extract all of the requested data sets of the broadcastdata service from a broadcast carousel included in the broadcast signal;a memory configured to store all of the requested data sets of thebroadcast data service, the requested data sets containing digitalaudio/video data and defining a plurality of digital audio/video datasets, the digital audio/video data sets including television clips; afirst controller configured to allow selection from a list of theplurality of sets of the digital audio/video data sets; and a secondcontroller responsive to a user initiated selection signal to cause thememory to output a user selected one of the plurality of digitalaudio/video data sets selected from the list, the selected one of theplurality of digital audio/video data sets having digital audio/videodata in non-real time, wherein the processor converts the digitalaudio/video data of the requested data sets of the broadcast dataservice into real time audio/video data, the broadcast data service istransmitted with broadcast digital television data as part of thebroadcast signal, and all of the broadcast digital television data is ina first data compression format, and all of the digital audio/visualdata sets are in a data compression format different from the firstformat.
 2. The system according to claim 1, wherein the digitalaudio/video data of the requested data sets of the broadcast dataservice is compressed and the processor decompresses the plurality ofsets off-line.
 3. The system according to claim 1, wherein digitalaudio/video data of the requested data sets of the broadcast dataservice is compressed and the processor conducts decompression using apredefined protocol.
 4. The system according to claim 1, wherein thedigital audio/video data of the requested sets of the broadcast dataservice is compressed and the processor conducts decompression using adownloaded protocol.
 5. The system according to claim 1, wherein theprocessor conducts off-line decryption of the broadcast data serviceusing a key.
 6. The system according to claim 1, wherein the memory is amagnetic hard disk drive or a semiconductor memory.
 7. The systemaccording to claim 1, further comprising a digital television receiverfor providing the broadcast signal to the processor.
 8. The systemaccording to claim 7, wherein at least the memory is separate from thedigital television receiver and linked by means of a network connection.9. The system according to claim 7, wherein the digital televisionreceiver selectively provides digital television data for display andwherein the processor extracts sets of the requested sets of thebroadcast data service irrespective of that display.
 10. The systemaccording to claim 1, wherein the second controller is also configuredto identify corresponding extracted and stored sets of the requesteddata sets and replaces sets in the memory with respective sets extractedfrom the broadcast signal.
 11. The system according to claim 10,wherein, if periodically, the broadcast signal includes all of therequested data sets of the broadcast data service, the second controllercan store all of the received requested sets in the memory.
 12. Thesystem according to claim 10, wherein the second controller accesses anadditional data channel to obtain and store in the memory all of thesets of the requested data sets of the broadcast data service.
 13. Thesystem according to claim 1, wherein the broadcast digital televisiondata is converted into real time audio/video data and transmitted inpackets generated according to an MPEG standard.
 14. The systemaccording to claim 13, wherein the MPEG standard is an MPEG2 standard.15. The system according to claim 1, wherein the memory outputs the userselected one of the plurality of digital audio/video data sets selectedfrom the list simultaneously with continued receipt of the broadcastdigital television data.
 16. The system according to claim 1, whereinthe selection signal is provided at any time during receipt of thebroadcast digital television data and independently of the broadcastdigital television data and the second controller is responsive at anytime during receipt of the broadcast digital television data andindependently of the broadcast digital television data to output saidselected portion.
 17. The system according to claim 1, wherein thebroadcast data service is broadcast on a separate channel to thebroadcast digital television data.
 18. The system according to claim 1,wherein the broadcast data service is broadcast on a different spectrumto the broadcast digital television data.
 19. The system according toclaim 1, wherein the digital audio/video data of the requested sets ofthe broadcast data service is configured in the broadcast signal forreception at a rate slower than an audio/video replay rate for theselected set.
 20. The system according to claim 1, wherein the digitalaudio/video data of the requested sets of the broadcast data service isbroadcast according to demand.
 21. The system according to claim 1,wherein the digital audio/video data of the requested sets of thebroadcast data service is cached locally after broadcast.
 22. The systemaccording to claim 1, further comprising: a transmitter configured totransmit to the broadcast headend an identity of each user selected oneof the plurality of digital audio/video data sets such that thebroadcast headend can determine demand for each set, wherein thebroadcast headend updates the plurality of digital audio/video data setswith a priority determined from a demand for each set.
 23. A receivercomprising: a receiving unit configured to receive a broadcast signal,including non-real time sets of broadcast data service, transmittedtogether with broadcast digital television data, and configured toextract the non-real time sets of the broadcast data service from thebroadcast signal; a memory configured to store the extracted non-realtime sets of the broadcast data service, the non-real time setscontaining digital audio/video data and defining a plurality of digitalaudio/visual data sets; a first controller configured to allow selectionfrom a list of the digital audio/video data sets; and a secondcontroller responsive to a selection signal to cause the memory tooutput a selected portion of the plurality of digital audio/visual datasets simultaneously with continued receipt of the broadcast digitaltelevision data, wherein the broadcast digital television data is in afirst data compression format, and the non-real time sets of thebroadcast data service are in a compression format different from thefirst format.
 24. The receiver according to claim 23, wherein thedigital audio/video data of the non-real time sets of the broadcast dataservice is compressed and the processor decompresses the plurality ofsets off-line.
 25. The receiver according to claim 23, wherein digitalaudio/video data of the non-real time sets of the broadcast data serviceis compressed and the receiving unit conducts decompression using apredefined protocol.
 26. The receiver according to claim 23, wherein thedigital audio/video data of the non-real time sets of the broadcast dataservice is compressed and the receiving unit conducts decompressionusing a downloaded protocol.
 27. The receiver according to claim 23,wherein the receiving unit conducts off-line decryption of the broadcastdata service using a key.
 28. The receiver according to claim 23,wherein the memory is a magnetic hard disk drive or a semiconductormemory.
 29. The receiver according to claim 23, further comprising adigital television receiver for providing the broadcast signal to thereceiving unit.
 30. The receiver according to claim 29, wherein at leastthe memory is separate from the digital television receiver and linkedby means of a network connection.
 31. The receiver according to claim29, wherein the digital television receiver selectively provides digitaltelevision data for display and wherein the receiving unit extracts thenon-real time sets of the broadcast data service irrespective of thatdisplay.
 32. The receiver according to claim 23, wherein the secondcontroller is also configured to identify corresponding extracted andstored non-real time sets and replaces sets in the memory withrespective sets extracted from the broadcast signal.
 33. The receiveraccording to claim 32, wherein, if periodically, the broadcast signalincludes all of the non-real time sets of the broadcast data service,the second controller can store all of the received non-real time setsin the memory.
 34. The receiver according to claim 32, wherein thesecond controller accesses an additional data channel to obtain andstore in the memory all of the non-real time sets of the broadcast dataservice.
 35. The receiver according to claim 23, wherein the broadcastdigital television data is converted into real time digital audio/videodata and transmitted in packets generated according to an MPEG standard.36. The receiver according to claim 35, wherein the MPEG standard is anMPEG2 standard.
 37. The receiver according to claim 23, wherein thebroadcast data service is transmitted together with the broadcastdigital television data.
 38. The receiver according to claim 23, whereinthe selection signal is provided at any time during receipt of thebroadcast digital television data and independently of the broadcastdigital television data and the second controller is responsive at anytime during receipt of the broadcast digital television data andindependently of the broadcast digital television data to output saidselected portion.
 39. The receiver according to claim 23, wherein thebroadcast data service is broadcast on a separate channel to thebroadcast digital television data.
 40. The receiver according to claim23, wherein the broadcast data service is broadcast on a differentspectrum to the broadcast digital television data.
 41. The receiveraccording to claim 23, wherein the digital audio/video data of thenon-real time sets of the broadcast data service is configured in thebroadcast signal for reception at a rate slower than an audio/videoreplay rate for the selected set.
 42. The receiver according to claim23, wherein the digital audio/video data of the non-real time sets ofthe broadcast data service is stored or transferred onto a portablestorage device.
 43. The receiver according to claim 23, wherein thereceiving unit assembles the digital audio/video data of the non-realtime sets of the broadcast data service for real-time display.
 44. Thereceiver according to claim 23, wherein the digital audio/video data ofthe non-real time sets of the broadcast data service is output in a fileformat corresponding to a file format of a selected device.